Climate Change: Day 19

October 28, 2014

  • Exam 3 is on Thursday, December 4th (final class period).

  • Exam 4 is on Friday, December 12th, 3-5p.

  • Term project is due Tuesday, December 9th. Email your HTML file to jelsner@fsu.edu.

No class next week Tuesday (Nov 4) and Thursday (Nov 6). I will be attending the AMS conference on severe local storms in Madison, WI. Use this time to get started on your term project.

Tornado and supercells thunderstorms.

What is a tornado?

Rotating column of air between a cloud and the ground. A funnel is visible rotation below the base of the cloud but the rotation is not reaching the ground.

Most (80%) tornadoes (EF0 & EF1) have winds weaker than 50 m/s (100 mph). These tornadoes account for 5% of all tornado deaths.

Strong (EF2 & EF3) tornadoes have winds from 50 to 73 m/s. Violent (EF4 & EF5 ) tornadoes have winds exceeding 73 m/s and are quite rare (about 1% of all tornadoes). The most violent tornadoes have winds exceeding 100 m/s.

Tornado damage path

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A tornado is assigned a single EF (Enhanced Fujita scale) damage rating based on the worst damage within the path.

Longer damage paths

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Damage path length/width by EF category alt text

What is a supercell thunderstorm?

A supercell thunderstorm is a rotating thunderstorm called a mesocyclone. alt text

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What makes a supercell rotate?

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Supercell rotation

Supercell rotation

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What makes a tornado?

  • The updraft of rising air near the ground weakens when the air from the rear flank downdraft (RFD) catches up to the air from the forward flank downdraft (FFD).

  • This stretches the rotating updraft and speeds the rotation.

  • Vortex stretching is not always enough to create a tornado (only 30% of all supercells produce tornadoes).

  • What else?

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Week by week tornado probability

Timmer and Cantore inside a tornado [17 min mark]

Estimating tornado intensity